Pipeline pig

ABSTRACT

A pipeline pig which is formed of an inflatable bladder and surrounding body is disclosed. Two embodiments are described and differ in the inclusion of means for preventing elongation of the bladder and loss of gauge of the pig. In one embodiment, a central member prevents elongation of the bladder. In the other embodiment, elongation of the bladder is prevented by incorporating non-extensible straps along the length of the bladder. A separate and removable exterior wear member is also provided. It can be replaced in the event that abrasion of the pipeline wears away its thickness.

United States Patent Knapp et al.

Feb. 4, 1975 PIPELINE PIG Primary Examiner-Edward L. Roberts Inventors: Kenneth M. Knapp; Charles C.

Knapp Jr., both of 1209 Hardy St., Houston, Tex. 77020 [57] ABSTRACT r A pipeline pig which is formed of an inflatable bladder Ffled' 1973 and surrounding body is disclosed. Two embodiments Appl. No: 377,389 are described and differ in the inclusion of means for preventing elongation of the bladder and loss of gauge of the pig. In one embodiment, a central member prevents elongation of the bladder. In the other embodi Field 104 06 ment, elongation of the bladder is prevented by incor- 3 porating non-extensible straps along the length of the bladder. A separate and removable exterior wear References Cited member is also provided. It can be replaced in the event that abrasion of the pipeline wears away its UNITED STATES PATENTS thickness. ,197 12/1961 Nehse et al. I. 15/l04.06 R

10 Claims, 5 Drawing Figures 3 24 F- j 36 Lu L}: --j /1 22 e r 20 28 am. i i r V V a (/40 V in Uh-n I6 PATENTEDFEB "41915 3,863,287

SHEET 10F 2 FIG] / 30 FIG. 2

PIPELINE PIG PRIOR ART Class 15. sub-class 104.06

BACKGROUND OF THE INVENTION In the cleaning and use of pipelines, pipeline pigs have assumed an important position. Pipeline pigs are relatively inexpensive for small diameter lines but their cost increases perhaps with the square or even the cube of pipeline diameter. This, of course. in part results from the cost of raw materials such as polyurethane, which cost is not insignificant.

A large diameter pig may be placed in a line and will travel several hundred miles. During the course of the trip, the pig is normally abraded by the rough pipe surface as it cleans the pipeline or separates batches of products. The abrasion of the pipeline against the pig wears away a portion of the surface. The wear is often distributed by incorporating angled edges on the pig to cause the pig to rotate. This prevents localization of the wear at the bottom of the pig and tends to wear the outer surface evenly. Even in this circumstance, the pig may wear losing only percent of its manufactured diameter, leaving the remaining 95 percent of the pig in tact, substantially without wear, and yet, in a condition requiring subsequent replacement. It is wasteful to discard a pig at this stage, and yet, it will not provide the same quality cleaning action. Inasmuch as pigs of substantial diameter will cost several hundred or thousand dollars, the economic waste resulting from this is not insignificant.

The apparatus of the present invention is directed to a pig which enables a portion of the pig to be re-used after the outer surface has been worn away. This enables some of the manufactured parts of the pig to be re-used to reduce the cost of cleaning or separation on a per mile basis. Moreover, it enables the user to control the gap or margin between a particular pig and the inner wall of the pipe. The pig can be inflated to higher internal pressures which swells the pig slightly even after a portion of the outer surface is worn away, thereby returning the pig close to its original gauge.

SUMMARY OF THE INVENTION Apparatus of the present invention is summarized as an inflatable pipeline pig which has a removable and reusable bladder. The pig is formed in two portions. An internal bladder is adapted to be inflated through a valve and pressured to some desired level. The bladder is formed of resilient material for ease of inflation. The bladder is constructed in the two embodiments to include means preventing its extension, which may reduce its diameter. Upon inflation to a specified pressure, the means mentioned above controls the length and prevents elongation. Control of the length is achieved in one embodiment by inclusion of an internal axial member which is connected to both ends of the bladder to prevent elongation. In the alternative embodiment, a plurality of straps about the length of the pig extending from end to end prevent elongation on inflation. The straps are preferably formed of a nonextensible material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side view ofa pig fabricated in accordance with the teachings of the present invention; FIG. 2 is a sectional view along the line 2 2 showing internal details of construction of a first embodiment of an inflatable pig having a removable bladder;

' FIG. 3 is a sectional view view along the line 3 3 of FIG. 2 showing internal details of construction of the first embodiment;

FIG. 4 is a sectional through an alternative embodiment similar to FIG. 2showing straps which prevent elongation of the bladder and pig; and

FIG. 5 is a sectional view along the line 5 5 of FIG. 4 illustrating internal details of construction of the alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is first directed to FIG. I of the drawings where the first embodiment 10 of the present invention is received within a pipe for cleaning or separation purposes. The pig 10 is formed of two major portions 14 and 16. The portion 14 is an outer body portion. The means 16 is a bladder which is placed in the outer body 14. The bladder 16 has a wall portion 18 of substantial thickness which is formed of a resilient material. The wall portion 18 connects with a back portion 20 and a nose portion 22. It forms a complete envelope or container. The numeral 24 identifies a cavity or chamber within the bladder 16 which is adapted to receive fluid under pressure for inflation of the bladder 16. A valve assembly 26 is located at the nose of the pig and includes a valve element and preferably a valve cover for the valve element. The valve element communicates with a passage 28 which opens into the interior chamber 24. The valve 26 permits filling of the bladder 16 through the passage 28 with fluid under pressure. Air or dry nitrogen is quite acceptable in most circumstances. However, incompressible fluids including water or oil can be used as desired.

The bladder 16 is particularly stout and able to receive a fluid therein at a pressure of several hundred psi. The range of pressure is fairly extreme and to this end, the wall 18 is preferably rather thick. It is formed of resilient material and able to expand slightly. Ordinarily, radial expansion of an inflatable member of this sort is usually accompanied by variations in the length of the pig. Variations in length are limited or controlled by the inclusion of a member 30 which extends from the nose 22 to the back 20. The member 30 limits lengthwise expansion of the pig. When the bladder 16 is inflated, some stretching of the bladder wall accompanies increase of internal pressure. As it stretches, it tends to elongate. If the elongation is prevented or limited, this limits expansion to the radial direction. This enables the use of the bladder to obtain controlled radial expansion. This is particularly advantageous in the situation where the outer surface of the pig wears away slowly by abrasion during use. More will be noted concerning this hereinafter.

The member 30 is preferably formed of the same material used to fabricate the bladder 16. For additional reinforcing, a flexible reinforcing member 32 is cast in the pig which flairs at each end to prevent elongation of the means 30. A non-extensible material is preferably used as the reinforcing member. For instance, fibrous materials can be used to provide the reinforcing member 32.

The bladder 16 is received in an outer body portion 14. The outer body is preferably cast around the bladder 16 after the bladder has been inflated to a nominal pressure. The outer body is preferably formed of polyurethane material for most applications. The bladder 16 is placed in a mold and is positioned an appropriate distance from the side walls of the mold so that the outer body 14 has a relatively uniform thick wall. The body 14 has a wall portion 30 which provides substantial strength and presents a surface which is abraded away during its use. The wall 30 is preferably formed of polyurethane to a hardness which measures from about forty to ninety durometer depending on the circumstances of application, size of the pig, and other factors. The side wall 30 is contoured to define a nose portion 32 which has a central recess 34 for enclosing the valve 26. The nose 32 is curved, more or less bullet shaped, and fairs smoothly into the body portion. The body portion 14 terminates at a back edge 36. A shallow recess 38 is formed at the back face. The pipe line pressure acts against a peripheral shoulder 40, tending to flair the back edge 36 slightly to maintain a good seal against the pipe 12.

The outer body 14 incorporates a number of diamond recesses 42, formed of angled edges 44 and 46. The remaining two edges of the diamond recess 42 are parallel to the edges 44 and 46. The angled edges cooperate to impart rotation to the pig as it traverses the pipeline. The rotation distributes wear on the pig. Without the rotation, the pig would tend to wear flat on the bottom portions. However, rotation distributes this wear about the full circumference. This extends the life of the pig.

As shown in FIG. 2, the recesses 42 do not penetrate fully through the wall 30. As the pig wears away, the wall portion 30 maintains the structural integrity to avoid exposure of the bladder 16 to surface abrasion.

After the pig has been used for some interval, the outer member 14 wears away. It is separated from the bladder 16. For instance, the bladder 16 can be deflated and the outer surface 14 cut away. The worn outer member 14 is discarded and the bladder 16 is available for subsequent re-use. Reusage is achieved by placing the bladder 16 in a mold and casting an additional outer body 14 about it. This permits the bladder to be used numerous times. The bladder is not normally bonded to the outer member, but they merely contact one another. The bladder approximates one-half of the weight of the embodiment and its re-usability reduces the cost of pigging a line over span of time.

Attention is next directed to FIG. 4 of the drawings which discloses an alternative embodiment indicated by the numeral 50. The embodiment 50 incorporates a bladder portion 52 and an outer covering portion 54. The outer portion 54 has the same exterior profile, bullet shaped nose, end lip and wall construction. It also incorporates similar diamond shaped recesses or angular edges which impart rotation during pigging. It dif fers in the construction of the bladder 52. The bladder 52 is similar at the nose portion and incorporates a closed body 56. It has a valve element 58 at the nose. Elongation of the bladder 52 is prevented by the installation of lengthwise straps 60 which are flexible but are formed of a non-extensible material. Several are included about the circumfrance of the'pig 50. Each straps 60 positioned on the exterior, elongation of the bladder is controlled. They also limit radial expansion of the bladder, although insufficiently to prevent the bladder from inflating and expanding to increase the diameter of the pig after the outer member 54 has worn somewhat.

The pigs 10 and both have the ability to increase in diameter by introducing fluid under pressure into the pigs. An increase in internal pressure produces an increase in pig diameter. Of course, an increase in pressure may be offset by an increase in pipeline pressure. Hence, pig diameter in the line is dependent on pressure differential across the pig.

The materials used in the fabrication of the pig presently illustrated preferably include polyurethane for the outer member. Other elastomers have been used successfully in other pigs and may be used in this pig also. The bladder is preferably formed of a more resilient material such as butadiene or other rubber-like plastics. The reinforcing straps and the reinforcing member 32 are flexible but non-extensible materials. One suitable material is polyester fiber in the molded elastomer. Another suitable material is coated metal cable.

The foregoing is directed to preferred embodiment of the present invention, the scope ofwhich is determined by the appended claims.

We claim:

1. A pipeline pig which comprises:

an inflatable elongate bladder means formed of a resilient wall which encloses a cayity; an outer body portion adapted to be placed about said bladder means and having an outer wall which is adapted to contact a pipeline and which is further adapted to be worn away by contact therewith; and, v

wherein said bladder means tends to expand on inflation and further including means limiting increases in length thereof.

2. The apparatus of claim 1 wherein said limiting means limits increases in length thereof commensurate with losses of diameter on inflation.

3. The apparatus of claim 2 wherein said limiting means comprises a longitudinally positioned member in said bladder means and connected to ends of said elongate bladder means.

4. The apparatus of claim 2 wherein said bladder means includes a closed wall portion connected to a nose and back end portion to define the cavity, said cavity enclosing said limiting means.

5. The apparatus of claim 4 wherein said limiting means includes an axially located member joined to the nose and back portions and is non-extensible.

6. The apparatus of claim 2 wherein said limiting means includes a flexible strap about said bladder means.

7. The apparatus of claim 6 wherein said strap is on the exterior of a closed body having a wall connected to a nose and back end portion.

8. A pipeline pig which comprises:

an inflatable elongate bladder means formed of a resilient wall which encloses a cavity;

an outer body portion adapted to be placed about said bladder means and inflated thereby, said outer body portion having an outer wall which is adapted to contact a pipeline and which is further adapted to be worn away by contact therewith; and,

5 6 a helically arranged edge along a portion of the helically arranged edge.

length of said outer body portion. 10. The apparatus of claim 8 including a second heli 9. The apparatus of claim 8 wherein said edge is decally arranged edge at an intersecting angle relative to fined adjacent to a recess in said outer wall which insaid first edge. cludes spaced interruption means which interrupt said 5 

1. A pipeline pig which comprises: an inflatable elongate bladder means formed of a resilient wall which encloses a cavity; an outer body portion adapted to be placed about said bladder means and having an outer wall which is adapted to contact a pipeline and which is further adapted to be worn away by contact therewith; and, wherein said bladder means tends to expand on inflation and further including means limiting increases in length thereof.
 2. The apparatus of claim 1 wherein said limiting means limits increases in length thereof commensurate with losses of diameter on inflation.
 3. The apparatus of claim 2 wherein said limiting means comprises a longitudinally positioned member in said bladder means and connected to ends of said elongate bladder means.
 4. The apparatus of claim 2 wherein said bladder means includes a closed wall portion connected to a nose and back end portion to define the cavity, said cavity enclosing said limiting means.
 5. The apparatus of claim 4 wherein said limiting means includes an axially located member joined to the nose and back portions and is non-extensible.
 6. The apparatus of claim 2 wherein said limiting means includes a flexible strap about said bladder means.
 7. The apparatus of claim 6 wherein said strap is on the exterior of a closed body having a wall connected to a nose and back end portion.
 8. A pipeline pig which comprises: an inflatable elongate bladder means formed of a resilient wall which encloses a cavity; an outer body portion adapted to be placed about said bladder means and inflated thereby, said outer body portion having an outer wall which is adapted to contact a pipeline and which is further adapted to be worn away by contact therewith; and, a helically arranged edge along a portion of the length of said outer body portion.
 9. The apparatus of claim 8 wherein said edge is defined adjacent to a recess in said outer wall which includes spaced interruption means which interrupt said helically arranged edge.
 10. The apparatus of claim 8 including a second helically arranged edge at an intersecting angle relative to said first edge. 